The invention relates to a filter, in particular an oil filter, according to the preamble of claim 1.
WO 94/23818 discloses a filter which has a filter element in the form of a zigzag-folded web material and a carrier casing which functions as a supporting body. The filter element forms a zigzag-fold arrangement which encloses the hollow-cylindrical carrier casing. The end folds of the filter element butt against one another and are connected to one another, in order to prevent unwanted flows between the contaminated side and the clean side of the filter element. The abutting end folds are connected securely by adhesive. Provided for this purpose is a recessed clamp in which there engage the end folds and ends of an expanded metal jacket which surrounds the zigzag-fold arrangement. In this case, said clamp forms a type of longitudinal seam clip which allows preliminary fixing of the expanded metal jacket and zigzag-fold arrangement, the then V-shaped ends of the expanded metal jacket and of the zigzag-fold arrangement forming a feed channel for the adhesive.
The problem here is that the sealing of the connection of the two end folds cannot be reliably ensured as a result of production tolerances in the case of adhesive bonding or stapling, with the result that flow medium which has not been cleaned can pass from the contaminated side into the clean side.
A further disadvantage is that, during the production of the filter, first of all the end folds have to be connected and then the web material has to be gathered together to give a zigzag-fold arrangement and, finally, the filter element has to be brought into abutment against the lateral surface of the carrier casing and fixed in this position. This large number of process steps prolongs the time required for production and also increases the number of possible sources of errors during the assembly of the filter.
The problem on which the invention is based is to design a filter of the generic type which can be mass-produced with a higher level of operational reliability.
This problem is solved according to the invention by the features of claim 1.
The clamping strip ensures that the end folds are held against one another with a defined clamping force which is of such a magnitude that unwanted flows between the contaminated side and clean side are prevented. The production speed can be increased because all that is required is for the end folds to be fitted into the clamping strip; furthermore, no further measures are necessary for a sealed termination of the two end folds, with the result that the filter is suitable in a particularly advantageous manner for mass production.
The clamping strip, which is arranged on the carrier casing, simplifies the assembly of the individual filter elements. The filter element is automatically connected to the carrier casing as soon as the end folds are fitted into the clamping strip. Additional filter-element-supporting components may be dispensed with or at least designed more simply.
According to a preferred embodiment, the clamping strip has approximately the same axial length as the carrier casing, with the result that the end folds of the filter element are reliably held together over the entire axial height of the filter.
The clamping strip expediently comprises two axially running clamping walls between which a clamping chamber is formed for receiving the end folds of the filter. On the side directed toward the clamping chamber, the advantageously mirror-symmetrical clamping walls each have a clamping nose via which the clamping pressure which is necessary for a sealed connection is applied. The clamping walls may enclose a small angle which opens in the radially outward direction, in order to facilitate the operation of fitting in the end folds.
In the filter folds of the filter element, it is possible to provide stamped formations which ensure that the walls of the filter folds, which are grouped in a zigzag arrangement around the carrier zone, do not butt directly against one another, but rather are fanned out radially and allow the medium which is to be cleaned to flow through. In order to receive the stamped formations in the end folds, there are provided in the clamping walls recesses which run in the longitudinal direction. The side surfaces of the two end folds fitted into the clamping strip can thus butt against one another with the smallest possible spacing between them.
The end sides of the carrier casing, of the clamping strip and of the filter element are expediently covered by end disks in order to separate the contaminated side from the clean side and in order to transfer to the stable carrier casing axial loading which acts on the filter. A sealed termination may be achieved by the end sides being secured in the end disk by plastification. In order to facilitate this operation of securing by plastification, provision is made for the end sides of the carrier casing and clamping strip each to have a plastification border, of which the wall thickness is reduced in relation to the wall thickness of the carrier casing and clamping strip. The thickness of the plastification border expediently corresponds to the thickness of the filter folds, with the result that, when the end side is pressed into the plastically deformable end disk, the clamping strip and the carrier casing provide approximately the same, reduced resistance as the filter element; this ensures that the end side is pressed uniformly into the end disk at right angles to the longitudinal axis of the filter.
Moreover, the tapered plastification border ensures that the end side is pressed into the end disk to a defined depth. A shoulder is formed between the plastification border and the respective end side of the wall of the carrier casing and/or clamping strip, and this shoulder indicates the maximum pressing-in depth. As soon as the shoulder comes into contact with the end disk, the pressure necessary for a pressing-in operation increases abruptly. With a predetermined, constant plastification pressure, this ensures that the pressing-in operation can only take place until there is abutment against the shoulder.